Add check to rgba-css-var function for body or bg

[mdo]

This is the most straightforward fix I can think of for this situation. It's definitely a my bad for not thinking about the new CSS var --body-rgb and there needing to be two separate CSS vars. This PR drops the --bs-body-rgb for two separate ones (so it's a small breaking change), but keeps the .bg-body and .text-body intact without change. it also required duplicating the utilities maps a bit—so we can differentiate at the Sass map level between bg and color. I think this is an acceptable solution, but definitely want to hear thoughts.

Fixes #34688.

/cc @ffoodd

[mdo]

Test failure seems unrelated, will re-run to see if I can get it to pass.

[ffoodd]

This works fine, and I can't find a better way through ATM 😄

[oliwerAR]

I've just stumbled on the .body-bg problem after update. But the proposed fix seems be a bit messy. Instead of messing with the rgba-css-var function and hardcoding and exepction, I think it would be better to leave rgba-css-var as it was before and use a consistent pattern in vaiables:

$utilities-text: map-merge(
  $utilities-colors,
  (
    "black": to-rgb($black),
    "white": to-rgb($white),
    "body-color": to-rgb($body-color)
  )
) !default;

$utilities-bg: map-merge(
  $utilities-colors,
  (
    "black": to-rgb($black),
    "white": to-rgb($white),
    "body-bg": to-rgb($body-bg)
  )
) !default;

It would be easier to understand what's going - the CSS var naming in particular.